1. Field of the Invention
The present invention relates to a laser device. More specifically, the present invention relates to a laser device the size of which can be reduced entirely.
2. Description of the Related Art
Conventionally, an yttrium-aluminum-garnet (YAG) crystal doped with neodymium (hereinafter, optionally referred to as xe2x80x9cNd:YAGxe2x80x9d) has been known as one of representative materials of a solid laser medium. In the yttrium-aluminum-garnet (YAG) crystal with neodymium, neodymium (Nd) is added (hereinafter, optionally referred to as xe2x80x9cdopedxe2x80x9d) as a laser active ion.
This is because the Nd:YAG crystal presents a variety of advantages when being used as a laser medium.
Namely, the Nd:YAG crystal has relatively large gain as a laser medium. Additionally, the Nd:YAG crystal has a variety of advantages such as chemical and physical stability, high mechanical strength, high thermal conductivity, applicability to a high-power laser device, an established method of crystal growth, and stable supply.
Incidentally, in recent years, a semiconductor laser (LD) pumped solid state laser device has been used as a laser device, in which a beam emitted from a laser diode is used as excited light, namely, excited light is emitted by semiconductor laser.
In such a semiconductor laser (LD) pumped solid state laser, a large absorption coefficient for pumping light is required as a characteristic of a laser crystal used as a laser medium.
A semiconductor laser (LD) pumped solid state laser can be made smaller in size, such as a micro chip laser or a single longitudinal mode laser. However, in order to efficiently downsize the semiconductor laser pumped solid state laser, it is necessary to use a laser crystal with a short absorption length for pumping light to largely absorb a beam from a laser diode in a short distance. For this reason, a laser crystal having a large absorption coefficient for pumping light is demanded as a laser medium.
Here, regarding the Nd:YAG crystal, when neodymium serving as a laser active ion is added, neodymium substitutes for an yttrium ion. However, in a conventional art, a maximum concentration is an atomicity ratio of about 1.3% and neodymium is not added by substituting an ion at a concentration higher than the maximum concentration.
Meanwhile, with an yttrium vanadate (hereinafter, optionally referred to gas xe2x80x9cYVOxe2x80x9d) crystal, which has been widely used as a laser medium of a semiconductor laser (LD) pumped solid state laser device, it is possible to readily add neodymium serving as a laser active ion at a high concentration, an atomicity ratio of about 3%.
Further, the Nd:YAG crystal, in which neodymium is added at a concentration of 1% in terms of atomicity ratio, has an absorption coefficient of about 8 cmxe2x88x921. Meanwhile, regarding the yttrium vanadate crystal doped with neodymium (hereinafter, optionally referred to as xe2x80x9cNd:YVO4xe2x80x9d), in which neodymium is added at a high-concentration of 3% of an atomicity ratio, it is possible to obtain a high absorption coefficient of about 40 cmxe2x88x921.
Hence, regarding an absorption length required for absorbing 90% of excited light, i.e., a length of a crystal, the Nd:YAG crystal with an absorption coefficient of about 8 cmxe2x88x921 requires a length of about 3 mm. Meanwhile, the Nd:YVO4 crystal with an absorption coefficient of about 40 cmxe2x88x921 only requires a length of about 0.5 mm.
As described above, the Nd:YVO4 crystal is characterized by a large absorption coefficient, which is required for the laser medium of a semiconductor laser (LD) pumped solid state laser device. On the other hand, the Nd:YVO4 crystal presents a large number of disadvantages when being used as a laser medium.
Namely, the Nd:YVO4 crystal is less likely to release heat because its thermal conductivity is about one third that of the Nd:YAG crystal. Moreover, on an upper laser level, the Nd:YVO4 crystal has a short life time of 90xcexc seconds as compared with the Nd:YAG crystal, resulting in small strage of energy. Further, because of its optical anisotropy, the Nd:YVO4 crystal is likely to be oscillated by specific polarization and is susceptible to thermal distortion. Other disadvantages are further presented such as difficulty in forming a crystal.
For this reason, the Nd:YVO4 crystal is preferable as a laser medium used for the semiconductor laser (LD) pumped solid state laser with low power and a small threshold value. However, regarding a laser medium used for the semiconductor laser (LD) pumped solid state laser with high power and a large threshold value for use in working and so on, even though the size is increased, the Nd:YAG crystal is used. Thus, the entire laser device is inevitably increased in size.
Therefore, a proposal has been strongly demanded on a laser device being able to entirely reduce the size thereof for micro chip lasers and single longitudinal mode lasers.
The present invention is devised to respond to the demand on the above-mentioned conventional art. An object of the present invention is to provide a laser device, which has an excellent characteristic originally exerted by an yttrium-aluminum-garnet crystal doped with neodymium and is reduced in size by using an entirely downsized laser medium.
In order to attain the above object, the present invention provides a laser device comprising a laser medium disposed in a resonator, in which excited light is incident upon the laser medium so as to cause laser oscillation in the resonator, and laser is emitted from the resonator, the laser medium being an yttrium-aluminum-garnet single crystal, in which neodymium is added as a laser active ion at a concentration exceeding an atomicity ratio of 1.3%.
Therefore, according to the present invention, the yttrium-aluminum-garnet single crystal, in which neodymium is added as a laser active ion at a concentration exceeding 1.3% in terms of atomicity ratio, is used as a laser medium. With such a laser medium composed of the yttrium-aluminum-garnet single crystal, in which neodymium is added at a high concentration, it is possible to obtain a high absorption coefficient relative to excited light. Thus, it is possible to provide an excellent characteristic originally exerted by the yttrium-aluminum-garnet crystal doped with neodymium and to entirely reduce the size thereof, thereby entirely downsizing the laser device.
In this case, in the above laser medium, the above neodymium may be added at a concentration of from 2% to 3% in terms of atomicity ratio.
Further, the excited light may be emitted by semiconductor lasers.
Moreover, the semiconductor laser excitation may be, for example, longitudinal excitation or transverse excitation.